Tunnel barrier layer, magnetoresistance effect element, method for manufacturing tunnel barrier layer, and insulating layer

ABSTRACT

A tunnel barrier layer includes a non-magnetic oxide, wherein a crystal structure of the tunnel barrier layer includes both an ordered spinel structure and a disordered spinel structure.

TECHNICAL FIELD

The present invention relates to a tunnel barrier layer, amagnetoresistance effect element, a method for manufacturing the tunnelbarrier layer, and an insulating layer.

Priority is claimed on Japanese Patent Application No. 2019-055048,filed Mar. 22, 2019, and Japanese Patent Application No. 2020-041278,filed Mar. 10, 2020, the content of which is incorporated herein byreference.

BACKGROUND ART

A giant magnetoresistance (GMR) element made up of a multilayer film ofa ferromagnetic layer and a non-magnetic layer, and a tunnelmagnetoresistance (TMR) element with an insulating layer (a tunnelbarrier layer, and a barrier layer) used for the non-magnetic layer areknown. In general, a TMR element has a higher element resistance but alarger magnetoresistance (MR) ratio than a GMR element. Attention hasbeen focused on TMR elements, as an element for a magnetic sensor, ahigh-frequency component, a magnetic head, and a nonvolatilemagnetoresistive random access memory (MRAM).

TMR elements can be classified into two types depending on a differencein the mechanism of tunnel conduction of electrons. One type is a TMRelement using only a bleeding effect (a tunnel effect) of a wavefunction between ferromagnetic layers. The other type is a TMR elementin which a coherent tunnel (in which only electrons having the symmetryof a specific wave function tunnel) in which the symmetry of the wavefunction is maintained is dominant. The TMR element in which coherenttunneling is dominant can obtain a larger MR ratio than a TMR elementusing only a tunnel effect.

MgO is an example of a tunnel barrier layer in which a coherent tunnelphenomenon occurs. As a material in lieu of MgO, for example, ternaryoxides (Mg—Al—O) made up of Mg, Al, and O are also being studied.Mg—Al—O has improved lattice matching with a ferromagnetic material ascompared with MgO, and even when a high voltage is applied, it isunlikely that an MR ratio will be lower than in conventional MgO.

For example, Japanese Patent No. 5586028 discloses an example in whichMgAl₂O₄ having a spinel-type crystal structure is used for a tunnelbarrier layer.

Further, Japanese Patent No. 5988019 discloses a ternary oxide (Mg—Al—O)having a cubic crystal (a disordered spinel structure) having half alattice constant of the spinel structure. Since the disordered spinelstructure is a metastable structure, the tunnel barrier layer can beformed without being limited to the stoichiometric composition of thespinel structure. In the disordered spinel structure, the latticeconstant can be continuously changed by adjusting the Mg—Al compositionratio. Further, Japanese Patent No. 5988019 discloses amagnetoresistance effect element in which a tunnel barrier layer havinga disordered spinel structure and a BCC-type Co—Fe-based ferromagneticlayer are combined. When the tunnel barrier layer having the disorderedspinel structure and the BCC-type Co—Fe-based ferromagnetic layer arecombined, a band folding effect is suppressed, and the magnetoresistanceeffect element stably exhibits a large MR ratio.

The tunnel barrier layer having the ordered spinel structure describedin Japanese Patent No. 5586028 cannot obtain a sufficiently large MRratio. Further, in the tunnel barrier layer having the disordered spinelstructure described in Japanese Patent No. 5988019, the MR ratio easilydecreases when a high voltage is applied. A large MR ratio and a highvoltage resistance are required to improve an output voltage of amagnetoresistance effect element.

In view of such circumstances, an object of the present invention is toprovide a magnetoresistance effect element capable of improving anoutput voltage.

SUMMARY OF THE INVENTION

The present inventors have introduced both an ordered spinel structureand a disordered spinel structure in the tunnel barrier layer. Thepresent invention provides the following means to solve theaforementioned problems.

(1) A tunnel barrier layer according to a first aspect includes anon-magnetic oxide, wherein a crystal structure of the tunnel barrierlayer includes both an ordered spinel structure and a disordered spinelstructure.

(2) In the tunnel barrier layer according to the aforementioned aspect,a lattice constant of the a disordered spinel structure may besubstantially half of a lattice constant of the ordered spinelstructure.

(3) The tunnel barrier layer according to the aforementioned aspect mayhave two or more of a first portion indicating a first electron beampattern, a second portion indicating a second electron beam pattern, anda third portion indicating a first pseudo electron beam pattern, innano-electron beam diffraction using a transmission electron microscope.

(4) In the tunnel barrier layer according to the aforementioned aspectconsists of a third portion indicating the first pseudo electron beampattern in nano-electron beam diffraction using a transmission electronmicroscope.

(5) In the tunnel barrier layer according to the aforementioned aspect,a ratio of the ordered spinel structure may be 10% or more and 90% orless.

(6) In the tunnel barrier layer according to the aforementioned aspect,a ratio of the ordered spinel structure may be 20% or more and 80% orless.

(7) In the tunnel barrier layer according to the aforementioned aspect,the non-magnetic oxide may include Mg and at least one of Al and Ga.

(8) The tunnel barrier layer according to the aforementioned aspect mayhave an oxide containing Mg and Ga, and an oxide containing Mg and Al,in which the oxide containing Mg and Ga may have the ordered spinelstructure, and the oxide containing Mg and Al may have the a disorderedspinel structure.

(9) In the tunnel barrier layer according to the aforementioned aspect,an orientation direction of the crystal may be a (001) orientation.

(10) A magnetoresistance effect element according to a second aspectincludes the tunnel barrier layer according to the aforementionedaspect, and a first ferromagnetic layer and a second ferromagnetic layersandwiching the tunnel barrier layer in a thickness direction.

(11) In the magnetoresistance effect element according to the secondaspect, at least one of the first ferromagnetic layer and the secondferromagnetic layer may contain elemental Fe.

(12) A method for manufacturing a tunnel barrier layer according to athird aspect includes first conditions in which oxygen sufficient toform an ordered spinel structure is supplied; and second conditions inwhich an amount of oxygen supply is smaller than in the firstconditions.

(13) An insulating layer according to a fourth aspect includes anon-magnetic oxide, wherein a crystal structure of the insulating layerincludes both an ordered spinel structure and a disordered spinelstructure.

The magnetoresistance effect element according to an aspect of thepresent invention has an improved output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a magnetoresistance effect elementaccording to an embodiment.

FIG. 2 shows a result obtained by performing nano-electron beamdiffraction (NBD) on an ordered spinel structure using a transmissionelectron microscope (TEM).

FIG. 3 shows a result obtained by performing nano-electron beamdiffraction (NBD) on the disordered spinel structure, using atransmission electron microscope (TEM).

FIG. 4 is a diagram showing a crystal structure of an ordered spinelstructure.

FIG. 5 is a diagram showing a crystal structure of a disordered spinelstructure.

FIG. 6 is a diagram showing an example of a crystal structure of atunnel barrier layer.

FIG. 7 is a diagram showing another example of the crystal structure ofthe tunnel barrier layer.

FIG. 8 is a diagram showing another example of the crystal structure ofthe tunnel barrier layer.

FIG. 9 is a cross-sectional view of a magnetic recording elementaccording to a first application example of the magnetoresistance effectelement.

FIG. 10 is a cross-sectional view of a magnetic recording elementaccording to a second application example of the magnetoresistanceeffect element.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the drawings as appropriate. In the drawings used in thefollowing description, there may be cases in which characteristic partsare enlarged for convenience to make the features of the presentinvention easy to understand, and dimensional ratios and the like of therespective components may be different from actual ones. Materials,dimensions, and the like shown in the following description are merelyexamples, and the present invention is not limited thereto, and can beimplemented with appropriate changes without departing from the scope ofthe invention.

‘Magnetoresistance Effect Element’

FIG. 1 is a cross-sectional view of a magnetoresistance effect elementaccording to the present embodiment. FIG. 1 is a cross-sectional view ofa magnetoresistance effect element 10 taken along a laminating directionof each layer of the magnetoresistance effect element. Themagnetoresistance effect element 10 has a first ferromagnetic layer 1, asecond ferromagnetic layer 2, and a tunnel barrier layer 3. Themagnetoresistance effect element 10 may have a cap layer, a base layer,and the like in addition to these layers. The tunnel barrier layer 3 isan example of an insulating layer.

(First Ferromagnetic Layer, and Second Ferromagnetic Layer)

The first ferromagnetic layer 1 and the second ferromagnetic layer 2 aremagnetic materials. The first ferromagnetic layer 1 and the secondferromagnetic layer 2 each have a magnetization. The magnetoresistanceeffect element 10 outputs a change in the relative angle between themagnetization of the first ferromagnetic layer 1 and the magnetizationof the second ferromagnetic layer 2 as a resistance change.

The magnetization of the second ferromagnetic layer 2 is, for example,harder to move than the magnetization of the first ferromagnetic layer1. When a predetermined external force is applied, the direction ofmagnetization of the second ferromagnetic layer 2 does not change (isfixed), and the direction of magnetization of the first ferromagneticlayer 1 changes. When the direction of magnetization of the firstferromagnetic layer 1 changes with respect to the direction ofmagnetization of the second ferromagnetic layer 2, a resistance value ofthe magnetoresistance effect element 10 changes. In this case, thesecond ferromagnetic layer 2 may be called a magnetization fixed layer,and the first ferromagnetic layer 1 may be called a magnetization freelayer. Hereinafter, a case in which the first ferromagnetic layer 1 is amagnetization free layer and the second ferromagnetic layer 2 is amagnetization fixed layer will be described as an example.

The first ferromagnetic layer 1 and the second ferromagnetic layer 2include a ferromagnetic material. The ferromagnetic material forming thefirst ferromagnetic layer 1 and the second ferromagnetic layer 2 is, forexample, a metal selected from a group consisting of Cr, Mn, Co, Fe andNi, an alloy containing at least one of these metals, and an alloycontaining these metals and elements of at least one kind or more fromB, C, and N. The first ferromagnetic layer 1 and the secondferromagnetic layer 2 contain, for example, an Fe element. The firstferromagnetic layer 1 and the second ferromagnetic layer 2 containingthe Fe element have high spin polarizability, and thus a MR ratio of themagnetoresistance effect element 10 increases. The first ferromagneticlayer 1 and the second ferromagnetic layer 2 are made of, for example,Fe, Co—Fe, Co—Fe—B, and Ni—Fe.

The first ferromagnetic layer 1 and the second ferromagnetic layer 2 maybe a Heusler alloy. The Heusler alloy is a half-metal and has high spinpolarizability. The Heusler alloy is an intermetallic compound having achemical composition of XYZ or X₂YZ, X is a transition metal element ora noble metal element from the Co, Fe, Ni, and Cu groups in the periodictable, Y is a transition metal from the Mn, V, Cr, and Ti groups or anelement type of X, and Z is a typical element from group III to group V.The Heusler alloy may be, for example, Co₂FeSi, Co₂FeGe, Co₂FeGa,Co₂MnSi, Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b), Co₂FeGe_(1-c)Ga_(c) or thelike.

The thicknesses of the first ferromagnetic layer 1 and the secondferromagnetic layer 2 are, for example, 3 nm or less. If the firstferromagnetic layer 1 and the second ferromagnetic layer 2 have a thinthickness, interfacial magnetic anisotropy occurs at an interfacebetween the first ferromagnetic layer 1, the second ferromagnetic layer2 and the tunnel barrier layer 3, and the directions of magnetization ofthe first ferromagnetic layer 1 and the second ferromagnetic layer 2 areeasily oriented in a direction perpendicular to a lamination plane.

An antiferromagnetic layer may be provided on a surface of the secondferromagnetic layer 2 on an opposite side to the tunnel barrier layer 3via a spacer layer. The second ferromagnetic layer 2, the spacer layer,and the antiferromagnetic layer have a synthetic antiferromagneticstructure (an SAF structure). The synthetic antiferromagnetic structureis made up of two magnetic layers sandwiching a non-magnetic layer.Since the second ferromagnetic layer 2 and the antiferromagnetic layerare antiferromagnetically coupled, a coercive force of the secondferromagnetic layer 2 becomes greater than that in a case of not havingan antiferromagnetic layer. The antiferromagnetic layer is, for example,IrMn, PtMn or the like. The spacer layer includes, for example, at leastone selected from the group consisting of Ru, Ir, and Rh.

(Tunnel Barrier Layer)

The tunnel barrier layer 3 contains a non-magnetic oxide. Thenon-magnetic oxide is, for example, an oxide containing Mg and at leastone of Al and Ga. The non-magnetic oxide is represented by, for example,Mg—(Al, Ga)—O. In the composition notation of the non-magnetic oxide,since a ratio between Mg and Al or Ga is not determined, the compositionis often described as above without using a subscript.

The tunnel barrier layer 3 has an ordered spinel structure and adisordered spinel structure as a crystal structure. The composition ofthe oxide forming the ordered spinel structure and the composition ofthe oxide forming the disordered spinel structure may be the same ordifferent. For example, the oxide forming the ordered spinel structuremay be an oxide (Mg—Ga—O) containing Mg and Ga, and the oxide formingthe disordered spinel structure may be an oxide (Mg—Al—O) containing Mgand Al.

FIG. 2 shows the result of performing nano-electron beam diffraction(NBD) on a crystal having the ordered spinel structure, using atransmission electron microscope (TEM). Further, FIG. 3 shows the resultof performing nano-electron beam diffraction (NBD) on a crystal havingthe disordered spinel structure, using s transmission electronmicroscope (TEM). The nano-electron beam diffraction measures theelectron pattern. The electron beam pattern is an electron imageobtained by irradiating a thin sample obtained by thinning themagnetoresistance effect element 10 with an electron beam narrowed to adiameter of about 1 nm, and transmitting and diffracting the electronbeam. FIGS. 2 and 3 show the results obtained by making the electronbeam incident on the [100] orientation of the thin sample. Hereinafter,the electron beam pattern shown in FIG. 2 is referred to as a firstelectron beam pattern, and the electron beam pattern shown in FIG. 3 isreferred to as a second electron beam pattern.

White portions shown in FIGS. 2 and 3 are diffraction spots in whichdiffracted light is detected, and are regularly arranged. Difference insizes of the diffraction spots are due to a distance from a central axisof the incident light, the diffraction easiness with respect to atoms asdiffraction points, and the like. The first electron beam pattern (FIG.2 ) is different from the second electron beam pattern (FIG. 3 ). Whenthe first electron beam pattern (FIG. 2 ) is compared with the secondelectron beam pattern (FIG. 3 ), spots S1, S2, S3, and S4 (hereaftercollectively referred to as “a first order spot”) observed in a regionsurrounded by dotted line increase in the first electron beam pattern(FIG. 2 ). In the first electron beam pattern, a brightness is equal inthe spots S1, S2, S3, and S4. Depending on the electron beam pattern,these is a case that the spots S1, S2, S3, and S4 have differentbrightness or a case that any of spots S1, S2, S3, and S4 are notobserved. The electron beam pattern of which the spots S1, S2, S3, andS4 have different brightness or any of spots S1, S2, S3, and S4 are notobserved means a first pseudo electron beam pattern.

The electron beam pattern can be regarded as a Fourier transform of thecrystal lattice, and observes changes in effective lattice constant andcrystal symmetry. A difference in the electron beam pattern between theordered spinel structure and the disordered spinel structure is due to adifference in the crystal structure between the ordered spinel structureand the disordered spinel structure.

FIG. 4 is a diagram showing a crystal structure of an ordered spinelstructure. In the ordered spinel structure, a site at which the elementA is ionized, and a site at which the element B is ionized are fixed,and the arrangement of these elements is regular. The element A is, forexample, one or more kinds of elements selected from the groupconsisting of Mg and Zn, and the element B is one or more kinds ofelements selected from the group consisting of Al, In, and Ga. Theelement A is, for example, Mg, and the element B is, for example, Al orGa. An oxide of Mg and Ga (Mg—Ga—O) is likely to have the ordered spinelstructure.

FIG. 5 is a diagram showing a crystal structure of a disordered spinelstructure. In the case of the disordered spinel structure, the ionizedelement A or element B can exist at any of a tetrahedral coordinationsite and an octahedral coordination site with respect to oxygen. Whichsite the element A or the element B enters is random. When the elementsA and B having different atomic radii randomly enter these sites, thecrystal structure becomes irregular. The disordered spinel structurehas, for example, the symmetry of a Fm-3m space group or the symmetry ofa F-43m space group. An oxide of Mg and Al (Mg—Al—O) is likely to have adisordered spinel structure.

An effective lattice constant (a/2) of the disordered spinel structureis substantially half of an effective lattice constant (a) of theordered spinel structure. For example, an actual lattice constant of thecrystal having the ordered spinel structure may be 0.808 nm, and asubstantial lattice constant of the crystal having the disordered spinelstructure is 0.404 nm. Here, the term “substantial lattice constant” isa case in which the lattice constant slightly changes due to oxygendeficiency or the like and is a lattice constant allowed whencrystallized as a spinel or a disordered spinel.

Here, the term “substantially” means an amount of lattice deviation thatdoes not cause loss of crystallinity, and includes a deviation of about3% on the basis of the value of the lattice constant. Further, the term“substantially half” includes a deviation of 4% around a half of thelattice constant (a) of the ordered spinel structure.

A difference in the effective lattice constant between the orderedspinel structure and the disordered spinel structure causes a differencein the electron beam pattern between the ordered spinel structure andthe disordered spinel structure. The second electron beam pattern (FIG.3 ) observes a basic reflection from a face-centered cubic (FCC)lattice. The first electron beam pattern (FIG. 2 ) observes reflectionfrom a {220} plane, in addition to the basic reflection from theface-centered cubic (FCC) lattice. The reflection from the {220} planecorresponds to the first order spots. When the ordered spinel structureand the disordered spinel structure are mixed, the diffraction intensityof the electron beam becomes weak, thereby a brightness in the orderspots decreases in a part of the order spots.

The thickness of the tunnel barrier layer 3 is, for example, 3 nm orless. When the thickness of the tunnel barrier layer 3 is 3 nm or less,the wave functions of the first ferromagnetic layer 1 and the secondferromagnetic layer 2 easily overlap each other beyond the tunnelbarrier layer 3, and the tunnel effect of the wave function between theferromagnetic layers and a coherent tunnel effect is easily obtained.

FIGS. 6 and 7 are diagrams showing an example of the crystal structureof the tunnel barrier layer 3. As described above, the tunnel barrierlayer 3 is, for example, 3 nm or less, and for example, in the case ofan ordered spinel structure having a lattice constant of 0.808 nm, thetunnel barrier layer 3 includes unit lattices of several layers. FIG. 6shows a case in which the unit lattice forming the tunnel barrier layer3 is one layer. FIG. 7 shows a case in which the unit lattice formingthe tunnel barrier layer 3 has a plurality of layers.

The tunnel barrier layer 3 shown in FIG. 6 has an ordered spinelstructure C1 and a disordered spinel structure C2. In the tunnel barrierlayer 3 shown in FIG. 6 , a region including only the ordered spinelstructure C1 is referred to as a first region R1, and a region includingonly the disordered spinel structure C2 is referred to as a secondregion R2. The first region R1 is an example of a first portion, and thesecond region R2 is an example of a second portion.

The first region R1 shows a first electron beam pattern in thenano-electron beam diffraction (NBD) using a transmission electronmicroscope (TEM). The second region R2 shows a second electron beampattern in the nano-electron beam diffraction (NBD) using thetransmission electron microscope (TEM).

Further, the tunnel barrier layer 3 shown in FIG. 7 also has the orderedspinel structure C1 and the disordered spinel structure C2. In thetunnel barrier layer 3 shown in FIG. 7 , a region including only theordered spinel structure C1 in the laminating direction is referred toas a first region R1, a region including only the disordered spinelstructure C2 in the laminating direction is referred to as a secondregion R2, a region laminated in the order of the ordered spinelstructure C1 and the disordered spinel structure C2 is referred to as athird region R3, and a region laminated in the order of the disorderedspinel structure C2 and the ordered spinel structure C1 is referred toas a fourth region R4. Further, a region laminated in the order of theordered spinel structure C1, the disordered spinel structure C2, and theordered spinel structure C1 is referred to as a fifth region R5, and aregion laminated in the order of the disordered spinel structure C2, theordered spinel structure C1, and the disordered spinel structure C2 isreferred to as a sixth region R6. The third region R3, the fourth regionR4, the fifth region R5, and the sixth region R6 are an example of athird portion. Since the crystal grows in the laminating direction, theprobability of occurrence of the third region R3, the fourth region R4,the fifth region R5, and the sixth region R6, in which different crystalstructures are laminated, is lower than the probability of occurrence ofthe first region R1 and the second region R2. The third region R3, thefourth region R4, the fifth region R5, and the sixth region R6 are amixed crystal including the ordered spinel structure and the disorderedspinel structure. The tunnel barrier layer 3 may consists of the firstregion R1 and one or more region selected from a group consisting of thethird region R3, the fourth region R4, the fifth region R5, and thesixth region R6. The tunnel barrier layer 3 may consists of the secondregion R2 and one or more region selected from a group consisting of thethird region R3, the fourth region R4, the fifth region R5, and thesixth region R6. Furthermore, as shown in FIG. 8 , the tunnel barrierlayer 3 may consists of one or more region selected from a groupconsisting of the third region R3, the fourth region R4, the fifthregion R5, and the sixth region R6.

The first region R1 shows a first electron beam pattern in thenano-electron beam diffraction (NBD), using the transmission electronmicroscope (TEM). The second region R2 shows a second electron beampattern in the nano-electron beam diffraction (NBD), using thetransmission electron microscope (TEM). The third region R3, the fourthregion R4, the fifth region R5, and the sixth region R6 show a firstpseudo electron beam pattern in the nano-electron beam diffraction(NBD), using the transmission electron microscope (TEM). The firstregion R1 is an example of the first portion. The second region R2 is anexample of the second portion. The third region R3, the fourth regionR4, the fifth region R5, and the sixth region R6 are an example of thethird portion.

The first order spots (the spots surrounded by the dotted line in FIG. 2) in the first electron beam pattern are caused by an ordered spinelstructure in which an effective lattice constant is approximately twicethat of the disordered spinel structure. In the first portion, the firstorder spot occurs in the electron beam pattern to form a first electronbeam pattern. Since the third region R3, the fourth region R4, the fifthregion R5, and the sixth region R6 include the ordered spinel structureC1, they show the order spot. However, the third region R3, the fourthregion R4, the fifth region R5, and the sixth region R6 form the firstpseudo electron beam pattern, since a peak intensity is changed in aposition thereof.

The first region R1 including only the ordered spinel structure shows afirst order spot having high brightness while being uniform, as comparedwith the third region R3 and the fourth region R4 partially having theordered spinel structure. As explained above, a spot obtained byirradiating the third region R3, the fourth region R4, the fifth regionR5, and the sixth region R6 with an electron beam may be thinner thanthe first order spot obtained by irradiating the first region R1 with anelectron beam (the diffraction intensity of the electron beam is weak),and a part of the first order spot may not be seen.

A ratio of the ordered spinel structure in the tunnel barrier layer 3 ispreferably equal to or greater than 10% and equal to or less than 90%,and more preferably, equal to or greater than 20% and equal to or lessthan 80%. A ratio occupied by the disordered spinel structure in whichthe second electron beam pattern is obtained in the tunnel barrier layer3 is preferably greater than 0% and equal to or less than 10% or equalto or greater than 90% and less than 100%, and more preferably, equal toor greater than 0% and equal to or less than 20% or equal to or greaterthan 80% and less than 100%.

A ratio of the ordered spinel structure in the tunnel barrier layer 3 isobtained as follows.

First, the magnetoresistance effect element 10 is cut along a planealong the laminating direction using a focused ion beam to produce athin sample of the magnetoresistance effect element 10. Next, tendifferent locations on the tunnel barrier layer 3 of the thin sample areirradiated with the electron beam of the transmission electronmicroscope (TEM), and nano-electron beam diffraction (NBD) is performedat each location. The ten locations irradiated with the electron beamdivide, for example, the tunnel barrier layer 3 into eleven sections atequal intervals in one direction in the plane, and set them to each ofpositions between adjacent sections.

Further, the electron beam patterns obtained from each of the tenlocations are separated into the first electron beam pattern and thefirst pseudo electron beam pattern, and the second electron beam patternby a presence or absence of spots. For each electron beam patternsobtained from the ten locations, a brightness is measured in spots S1 toS4. For each ten locations, an average of the brightness of the spots S1to S4 (the brightness average) is measured, when a brightness of onespot having a highest brightness in the spots S1 to S4 is determined100. In each ten locations, the average of the brightness of the spotsS1 to S4 shows a ratio of the ordered spinel structure. Accordingly, anaverage calculated from the ratios of the ordered spinel structure inthe electron beam patterns of the ten locations is a ratio of theordered spinel structure in the tunnel barrier layer 3.

Further, the tunnel barrier layer 3 is preferably (001) oriented. Thetunnel barrier layer 3 may be a (001) oriented single crystal or may bea polycrystal mainly containing a (001) oriented crystal. When thetunnel barrier layer 3 is (001) oriented, the lattice matching with thefirst ferromagnetic layer 1 and the second ferromagnetic layer 2 isenhanced, and the coherent tunnel effect is easily obtained. Inparticular, when the first ferromagnetic layer 1 or the secondferromagnetic layer 2 is Fe, Co—Fe, a Co-based Heusler alloy or the likecontaining an Fe element, the lattice matching is enhanced.

The magnetoresistance effect element 10 has, for example, a columnarshape. The magnetoresistance effect element 10 has, for example, acircular shape, an elliptical shape, a square shape, a triangular shape,and a polygonal shape in a plan view from the laminating direction. Itis preferable that the shape of the magnetoresistance effect element 10in a plan view from the laminated direction be circular or ellipticalfrom the viewpoint of symmetry.

A length of a long side of the magnetoresistance effect element 10 in aplan view from the laminating direction is preferably equal to or lessthan 80 nm, more preferably equal to or less than 60 nm, and even morepreferably equal to or less than 30 nm. If the length of the long sideis equal to or less than 80 nm, it is difficult to form a domainstructure in the ferromagnetic material, and it is not necessary toconsider a component different from the spin polarization in theferromagnetic metal layer.

Further, if the length of the long side is equal to or less than 30 nm,a single domain structure is formed in the ferromagnetic layer, and themagnetization reversal speed and the probability are improved. Inaddition, there is a strong demand for a low resistance especially inminiaturized magnetoresistance effect elements.

Next, a method for manufacturing the magnetoresistance effect element 10according to the present embodiment will be described. Themagnetoresistance effect element 10 is obtained by sequentiallylaminating the first ferromagnetic layer 1, the tunnel barrier layer 3,and the second ferromagnetic layer 2. The method for forming each layerincludes, for example, a sputtering method, an evaporation method, alaser ablation method and a molecular beam epitaxy (MBE) method.

The tunnel barrier layer 3 has film formation conditions of firstconditions and second conditions. The tunnel barrier layer 3 is, forexample, formed under the first condition and then formed under thesecond condition. Further, the tunnel barrier layer 3 may be formed, forexample, under the second condition and then formed under the firstcondition.

The first condition is a film formation condition in which oxygensufficient to form the ordered spinel structure is supplied to a layerserving as the tunnel barrier layer 3. For example, when an alloy islaminated and the alloy is sufficiently oxidized, the tunnel barrierlayer 3 is obtained. The oxidation is, for example, a plasma oxidationor an oxidation performed by oxygen introduction. The tunnel barrierlayer 3 has an ordered spinel structure when sufficient oxygen issupplied.

Whether the ionized element A and the element B enter a tetrahedralcoordination site or an octahedral coordination site with respect tooxygen is greatly affected by the energy potential. When sufficientoxygen is supplied to the tunnel barrier layer 3, from the viewpoint ofenergy potential, the sites in which each of the ionized elements A andB are stabilized are fixed, and the ordered spinel structure isstabilized.

The amount of oxygen sufficient to form the ordered spinel structure canbe obtained from the amount of oxygen theoretically taken in from thecomposition formula. For example, when oxygen in excess of the amount ofoxygen theoretically taken in from the composition formula is suppliedinto the oxidation treatment chamber, oxygen sufficient to form anordered spinel structure is taken into the layer serving as the tunnelbarrier layer 3. The amount of oxygen taken into the layer serving asthe tunnel barrier layer 3 can be freely controlled by adjusting, forexample, the flow rate of oxygen introduced into the oxidation treatmentchamber, the pressure of the oxidation treatment chamber, the oxidationtime, and the amount of oxygen with respect to the composition of thetarget alloy. For example, under the first condition, the pressure inthe oxidation treatment chamber is set to 100 Pa.

The second condition is a condition in which the amount of oxygensupplied to the layer serving as the tunnel barrier layer 3 is smallerthan in the first condition. If the amount of supply of oxygen isinsufficient, the tunnel barrier layer 3 has a disordered spinelstructure.

When oxygen is deficient in the tunnel barrier layer 3, oxygen is one ofthe elements that contribute to the crystal lattice, and the crystalstructure is disturbed. When the crystal structure is disturbed, theenergy states at the sites in which the tetrahedral coordination or theoctahedral coordination with respect to oxygen is performed are alsodisturbed. When the energy state is disturbed, the element A supposed tobe stabilized at the site in which the tetrahedral coordination isperformed with respect to oxygen is stabilized at the site in which theoctahedral coordination is performed with respect to oxygen, or viceversa. Therefore, which site the element A and the element B enter isentirely random, and as a result, it is easy to stabilize with a moredisordered spinel structure.

The second condition, for example, reduces the flow rate of oxygen to beintroduced into the oxidation treatment chamber from the firstcondition.

As another example, the second condition sets the pressure of theoxidation treatment chamber to be lower than the first condition. Asanother example, the second condition sets the oxidation time to beshorter than in the first condition. As another example, the secondcondition reduces the amount of oxygen with respect to the compositionof the target alloy. For example, under the second condition, thepressure in the oxidation treatment chamber is set to 1 Pa.

Since the tunnel barrier layer 3 is thin, even if the first conditionand the second condition are sequentially performed, the ordered spinelstructure and the disordered spinel structure are mixed in the tunnelbarrier layer 3. The tunnel barrier layer 3 may be heated after the filmformation.

Next, an application example of the magnetoresistance effect element 10according to the embodiment will be described. The magnetoresistanceeffect element 10 can be used for, for example, a magnetic sensor, amemory such as an MRAM, or the like.

FIG. 9 is a cross-sectional view of a magnetic recording element 100according to a first application example. FIG. 9 is a cross-sectionalview of the magnetoresistance effect element 10 taken along thelaminating direction of each layer of the magnetoresistance effectelement. The magnetic recording element 100 shown in FIG. 9 is anexample of an application example of the magnetoresistance effectelement 10.

The magnetic recording element 100 has the magnetoresistance effectelement 10, a first electrode 11, a second electrode 12, a power supply13, and a measuring unit 14. The first electrode 11 is connected to afirst surface of the magnetoresistance effect element 10 in thelaminating direction. The second electrode 12 is connected to a secondsurface of the magnetoresistance effect element 10 in the laminatingdirection. The first electrode 11 and the second electrode 12 areconductors, for example, made of Cu. The power supply 13 and themeasuring unit 14 are connected to the first electrode 11 and the secondelectrode 12, respectively. The power supply 13 gives a potentialdifference in the laminating direction of the magnetoresistance effectelement 10. The measuring unit 14 measures a resistance value of themagnetoresistance effect element 10 in the laminating direction.

When a potential difference is generated between the first electrode 11and the second electrode 12 by the power supply 13, a current flows inthe laminating direction of the magnetoresistance effect element 10. Thecurrent is spin-polarized when passing through the second ferromagneticlayer 2, and turns to a spin polarization current. The spin polarizationcurrent reaches the first ferromagnetic layer 1 via the tunnel barrierlayer 3. The magnetization of the first ferromagnetic layer 1 undergoesa magnetization reversal by receiving a spin transfer torque (STT) dueto the spin polarization current. When a direction of magnetization ofthe first ferromagnetic layer 1 and a direction of magnetization of thesecond ferromagnetic layer 2 change, the resistance of themagnetoresistance effect element 10 in the laminating direction changes.A resistance value of the magnetoresistance effect element 10 in thelaminating direction is read by the measuring unit 14. That is, themagnetic recording element 100 shown in FIG. 9 is a spin transfer torque(STT) type magnetic recording element.

FIG. 10 is a cross-sectional view of a magnetic recording element 101according to a second application example. FIG. 10 is a cross-sectionalview of the magnetoresistance effect element 10 taken along thelaminating direction of each layer of the magnetoresistance effectelement. The magnetic recording element 101 shown in FIG. 10 is anexample of an application example of the magnetoresistance effectelement 10.

The magnetic recording element 101 has a magnetoresistance effectelement 10, a first electrode 21, a first wiring 22, a power supply 23,and a measuring unit 24. The first electrode 21 is connected to a firstsurface of the magnetoresistance effect element 10 in the laminatingdirection. The first wiring 22 is connected to a second surface of themagnetoresistance effect element 10 in the laminating direction. Thefirst electrode 21 is a conductor, for example, made of Cu. The firstwiring 22 includes one of a metal, an alloy, an intermetallic compound,a metal boride, a metal carbide, a metal silicide, and a metal phosphidehaving a function of generating a spin current by a spin Hall effectwhen the current flows. The first wiring 22 is, for example, anon-magnetic metal of an atomic number 39 or more having d electrons orf electrons on an outermost shell. The power supply 23 is connected tothe first end and the second end of the first wiring 22.

The measuring unit 24 is connected to the first electrode 21 and thefirst wiring 22 to measure a resistance value of the magnetoresistanceeffect element 10 in the laminating direction.

When a potential difference occurs between the first end and the secondend of the first wiring 22 by the power supply 23, the current flowsalong the first wiring 22. When the current flows along the first wiring22, a spin Hall effect occurs due to spin orbit interaction. The spinHall effect is a phenomenon in which a moving spin is bent in adirection orthogonal to a flow direction of the current. The spin Halleffect causes uneven distribution of spins in the first wiring 22 andinduces a spin current in the thickness direction of the first wiring22. The spin is injected from the first wiring 22 into the firstferromagnetic layer 1 by the spin current.

The spin injected into the first ferromagnetic layer 1 gives a spinorbit torque (SOT) to the magnetization of the first ferromagnetic layer1. The first ferromagnetic layer 1 receives the spin orbit torque (SOT)and reverses the magnetization. When the direction of magnetization ofthe first ferromagnetic layer 1 and the direction of magnetization ofthe second ferromagnetic layer 2 change, the resistance value of themagnetoresistance effect element 10 in the laminating direction changes.The resistance value of the magnetoresistance effect element 10 in thelaminating direction is read by the measuring unit 14. That is, themagnetic recording element 101 shown in FIG. 10 is a spin-orbit torque(SOT) type magnetic recording element.

The magnetoresistance effect element 10 according to the presentembodiment can output a larger output voltage, for example, than a casein which the tunnel barrier layer 3 has only the ordered spinelstructure. A large MR ratio and a high voltage resistance are requiredto improve the output voltage of the magnetoresistance effect element.Since the crystal structure of the ordered spinel structure is morestable than that of the disordered spinel structure, the MR ratio ishard to decrease even when a large voltage is applied. On the otherhand, the disordered spinel structure can increase the MR ratio ascompared with the ordered spinel structure. This is because theeffective lattice constant of the disordered spinel structure is reducedby half as compared with the ordered spinel structure, and the latticematching with the first ferromagnetic layer 1 and the secondferromagnetic layer 2 is easily increased. Since the ordered spinelstructure and the disordered spinel structure are mixed in themagnetoresistance effect element 10 according to the present embodiment,the characteristics of each structure can be compatible. Accordingly,the magnetoresistance effect element 10 according to the presentembodiment has a large MR ratio and a high voltage resistance, and theoutput voltage thereof is improved.

EXAMPLE Example 1

The magnetoresistance effect element 10 shown in FIG. 1 was manufacturedon an MgO (001) single crystal substrate. First, 40 nm of Cr waslaminated as a base layer on the substrate, and a heat treatment wasperformed at 800° C. for an hour. 30 nm of Fe was laminated as the firstferromagnetic layer 1 and the heat treatment was performed at 300° C.for 15 minutes.

Next, a 0.5 nm film of an alloy represented by Mg_(0.33)Al_(0.67) wasformed on the first ferromagnetic layer 1 and subjected to a naturaloxidation. The natural oxidation was performed by exposing the alloy toair of a pressure of 100 Pa for 600 seconds (the first condition).Thereafter, a 0.5 nm film of an alloy represented by Mg_(0.33)Al_(0.67)was formed, and the natural oxidation was performed by exposing thealloy to air of a pressure of 1 Pa for 600 seconds (the secondcondition). Thereafter, the laminated film was subjected to the heattreatment in a vacuum at 400° C. for 15 minutes to obtain a tunnelbarrier layer 3 (Mg—Al—O layer).

Next, 6 nm of Fe was laminated as the second ferromagnetic layer 2 onthe tunnel barrier layer 3 and the heat treatment was performed at 350°C. for 15 minutes to obtain a magnetic tunnel junction. Next, a 12 nmfilm of IrMn was formed as an antiferromagnetic layer, and a 20 nm filmof Ru was formed as a cap layer to obtain a magnetoresistance effectelement 10. Finally, a heat treatment was performed at a temperature of175° C. for 30 minutes while applying a magnetic field of 5 kOe toimpart uniaxial magnetic anisotropy to the second ferromagnetic layer 2.The magnetoresistance effect element 10 was formed in a columnar shapeof a diameter of 80 nm.

The magnetoresistance effect element 10 manufactured using the focusedion beam was cut on a surface along the laminating direction, and a thinsample of the tunnel barrier layer 3 was manufactured. Further, a thinsample was subjected to nano-electron beam diffraction (NBD), using thetransmission electron microscope (TEM). Specifically, the thin samplewas irradiated with an electron beam narrowed to a diameter of about 1nm, and an electron beam pattern obtained by transmission diffractionwas measured. Further, in the electron beam pattern observing the spot,the brightness of the spot was measured by using an image analysissoftware. The electron beam was applied to ten locations of the tunnelbarrier layer 3. The ten locations irradiated with the electron beamdivide the tunnel barrier layer 3 into eleven sections at equalintervals in one direction in the plane, and correspond to respectivepositions between the adjacent sections. The electron beam was incidentin the direction of Mg—Al—O [100].

Five among the electron beam patterns measured at each of the tenlocations were the first electron beam patterns, and the remaining fivewere the second electron beam patterns. The ratio occupied by theordered spinel structure and the disordered spinel structure in thetunnel barrier layer 3 was 50%, respectively.

Examples 2 to 5

Examples 2 to 5 are different from Example 1 in that the manufacturingconditions of the tunnel barrier layer 3 are changed from Example 1.Other conditions were the same, and the electron beam pattern wasmeasured at ten locations.

Example 2 is different from Example 1 in that the thickness of the alloyrepresented by Mg_(0.33)Al_(0.67) naturally oxidized under the firstcondition was 0.1 nm, and the thickness of the alloy represented byMg_(0.33)Al_(0.67) naturally oxidized under the second condition was 0.9nm. One of the electron beam patterns measured at each of the tenlocations was the first electron beam pattern, and the remaining ninewere the second electron beam patterns. The ratio occupied by theordered spinel structure in the tunnel barrier layer 3 was 10%, and theratio occupied by the disordered spinel structure was 90%.

Example 3 is different from Example 1 in that the thickness of the alloyrepresented by Mg_(0.33)Al_(0.67) naturally oxidized under the firstcondition was 0.2 nm, and the thickness of the alloy represented byMg_(0.33)Al_(0.67) naturally oxidized under the second condition was 0.8nm. Two of the electron beam patterns measured at each of the tenlocations were the first electron beam patterns, and the remaining eightwere the second electron beam patterns. The ratio occupied by theordered spinel structure in the tunnel barrier layer 3 was 20%, and theratio occupied by the disordered spinel structure was 80%.

Example 4 is different from Example 1 in that the thickness of the alloyrepresented by Mg_(0.33)Al_(0.67) naturally oxidized under the firstcondition was 0.8 nm, and the thickness of the alloy represented byMg_(0.33)Al_(0.67) naturally oxidized under the second condition was 0.2nm. Eight of the electron beam patterns measured at each of the tenlocations were the first electron beam patterns, and the remaining twowere the second electron beam patterns. The ratio occupied by theordered spinel structure in the tunnel barrier layer 3 was 80%, and theratio occupied by the disordered spinel structure was 20%.

Example 5 is different from Example 1 in that the thickness of the alloyrepresented by Mg_(0.33)Al_(0.67) naturally oxidized under the firstcondition was 0.9 nm, and the thickness of the alloy represented byMg_(0.33)Al_(0.6)7 naturally oxidized under the second condition was 0.1nm. Nine of the electron beam patterns measured at each of the tenlocations were the first electron beam patterns, and the remaining onewas the second electron beam pattern. The ratio occupied by the orderedspinel structure in the tunnel barrier layer 3 was 90%, and the ratiooccupied by the disordered spinel structure was 10%.

Comparative Example 1

In Comparative Example 1, when laminating the tunnel barrier layer 3, afilm 1.0 nm of an alloy represented by Mg_(0.33)Al_(0.6)7 was formed andsubjected to natural oxidation. The natural oxidation was performed byexposure to air at a pressure of 1 Pa for 600 seconds. ComparativeExample 1 differs from Example 1 in that the film formation and thenatural oxidation of the alloy were performed at a time. All theelectron beam patterns measured at each of the ten locations were thesecond electron beam patterns. The ratio occupied by the ordered spinelstructure in the tunnel barrier layer 3 was 0%, and the ratio occupiedby the disordered spinel structure was 100%.

Comparative Example 2

In Comparative Example 2, when laminating the tunnel barrier layer 3, afilm 1.0 nm of an alloy represented by Mg_(0.33)Al_(0.67) was formed andsubjected to natural oxidation. The natural oxidation was performed byexposure to air at a pressure of 100 Pa for 600 seconds. ComparativeExample 1 differs from Example 1 in that the film formation and thenatural oxidation of the alloy were performed at a time. All theelectron beam patterns measured at each of the ten locations were thefirst electron beam patterns. The ratio occupied by the ordered spinelstructure in the tunnel barrier layer 3 was 100%, and the ratio occupiedby the disordered spinel structure was 0%.

The MR ratios of the magnetoresistance effect elements of Examples 1 to5 and Comparative Examples 1 and 2 were measured, respectively. Themeasurement was performed at 300 K (room temperature). The outputvoltages of the magnetoresistance effect elements of Examples 1 to 5 andComparative Examples 1 and 2 were also determined. The MR ratio and theoutput voltage were determined on the basis of the following formula.The output voltage was determined from the MR ratio and the appliedvoltage when applying a voltage (V_(half)) at which the MR ratio wasreduced by half.“MR ratio (%)”=(R _(AP) −R _(P))/R _(P)×100“Output voltage”=½V _(bias)(TMR(V)/1+TMR(V))

R_(P) is a resistance when the magnetization directions of the firstferromagnetic layer 1 and the second ferromagnetic layer 2 are parallel,and R_(AP) is a resistance when the magnetization directions of thefirst ferromagnetic layer 1 and the second ferromagnetic layer 2 areantiparallel. TMR is (R_(AP)−R_(P))/RP.

V_(bias) is an applied voltage, which is a voltage (V_(half)) at whichthe MR ratio is reduced by half. TMR (V) is an MR ratio when a voltageis applied. The voltage characteristics were determined by firstmeasuring the MR ratio when applying a low voltage of 1 mV and byincreasing the applied voltage. The results thereof are summarized inTable 1 below.

TABLE 1 First portion TMR Output ratio MR Vhalf (V) voltage (%) (%) (V)(%) (V) Comparative 0 183 1 92 0.24 example 1 Example 2 10 179 1.3 1070.31 Example 3 20 181 1.47 123 0.35 Example 1 50 175 1.46 123 0.34Example 4 80 179 1.46 122 0.34 Example 5 90 159 1.4 107 0.31 Comparative100 136 1.38 88 0.28 example 2

As can be seen from Table 1, the magnetoresistance effect elements shownin Examples 1 to 5 were superior in output voltage to themagnetoresistance effect elements shown in Comparative Examples 1 and 2.

EXPLANATION OF REFERENCES

-   -   1 First ferromagnetic layer    -   2 Second ferromagnetic layer    -   3 Tunnel barrier layer    -   10 Magnetoresistance effect element    -   11, 21 First electrode    -   12 Second electrode    -   22 First wiring    -   13, 23 Power supply    -   14, 24 Measuring unit

What is claimed is:
 1. A tunnel barrier layer comprising: a non-magneticoxide, wherein a crystal structure of the tunnel barrier layer includesboth an ordered spinel structure and a disordered spinel structure, andthe ordered spinel structure shows a reflection from a body-centeredcubic (FCC) lattice and a reflection from a {220} plane in anano-electron beam diffraction using a transmission electron microscope.2. The tunnel barrier layer according to claim 1, wherein a latticeconstant of the disordered spinel structure is substantially half of alattice constant of the ordered spinel structure.
 3. The tunnel barrierlayer according to claim 1, further comprising: two or more of a firstportion indicating a first electron beam pattern, a second portionindicating a second electron beam pattern, and a third portionindicating a first pseudo electron beam pattern, in nano-electron beamdiffraction using a transmission electron microscope.
 4. The tunnelbarrier layer according to claim 1, consisting of a third portionindicating the first pseudo electron beam pattern in nano-electron beamdiffraction using a transmission electron microscope.
 5. The tunnelbarrier layer according to claim 1, wherein a ratio of the orderedspinel structure is 10% or more and 90% or less.
 6. The tunnel barrierlayer according to claim 1, wherein a ratio of the ordered spinelstructure is 20% or more and 80% or less.
 7. The tunnel barrier layeraccording to claim 1, wherein the non-magnetic oxide includes Mg and atleast one of Al and Ga.
 8. The tunnel barrier layer according to claim1, further comprising: an oxide containing Mg and Ga, and an oxidecontaining Mg and Al, wherein the oxide containing Mg and Ga has theordered spinel structure, and the oxide containing Mg and Al has thedisordered spinel structure.
 9. The tunnel barrier layer according toclaim 1, wherein an orientation direction of the crystal is a (001)orientation.
 10. A magnetoresistance effect element comprising: thetunnel barrier layer according to claim 1; and a first ferromagneticlayer and a second ferromagnetic layer sandwiching the tunnel barrierlayer in a thickness direction.
 11. The magnetoresistance effect elementaccording to claim 10, wherein at least one of the first ferromagneticlayer and the second ferromagnetic layer contains an Fe element.
 12. Amethod for manufacturing a tunnel barrier layer according to claim 1,comprising: a first condition in which oxygen sufficient to form anordered spinel structure is supplied; and a second condition in which anamount of oxygen supply is smaller than in the first condition.